1. Field of the Invention
The present invention relates generally to thermotropic liquid crystal polymer microcapsules, a method for preparing the same, and cosmetic compositions containing the same. More particularly, the present invention relates to thermotropic liquid crystal polymer microcapsules which can show behavior of a liquid crystal in the polymer phase due to phase separation between liquid crystal and polymer, therefore, can be incorporated into cosmetic composition as an additive for visual effect, and can improve the stability of the active ingredients in cosmetic base by loading the active ingredients within the liquid crystal, and relates to a method for preparing the same.
2. Description of the Related Arts
Liquid crystal shows unique arrangement in electric field, and therefore, it is used in display of electric apparatus such as projector, computer and television. Further, it has been incorporated in the cosmetic composition for improving protective function of stratum corneum and for increasing moisture retention and softness of the skin. Additionally, some liquid crystals, because of structural regularity, can scatter light to show beautiful colors and thereby provide unique appearance. Therefore, liquid crystals have been extensively used in the cosmetic field.
Conventionally, liquid crystals, in order to be protected from contaminants, oxidants and radiations or to provide novel functions, were encapsulated by polymers. And, extensive studies on encapsulation of liquid crystals have been conducted.
For examples, Japanese Patent Laid-open publication No. 61-502128 disclosed a method for encapsulating liquid crystal, which comprises steps of mixing liquid crystal with thermosetting resin, and then hardening the resin to be separated from liquid crystal. And, U.S. Pat. No. 4,285,720, No. 4,155,741 and No. 4,046,741 disclosed a method for preparing polyurea microcapsules by interfacial polymerization of polyisocyanate as an intermediate.
However, it is impossible to observe unique behavior of liquid crystal, i.e. orientation of liquid crystal in the microcapsules provided by these conventional methods, because liquid crystals are dispersed within polymer phase without separation thereof.
In addition, in case of thermotropic liquid crystal that was applied to smart system, because its behavior depends on environmental change such as temperature, the behavior became diluted by the addition of solvent or migration into hydrophobic phase, and therefore, sometimes encapsulation was impossible.
Under this circumstance, the present inventors have conducted extensive studies on encapsulation of liquid crystal of which behavior can be observed as it is. As a result thereof, we found that by encapsulating cholesterol-type thermotropic liquid crystal and monomer with suspension polymerization method, compatibility between liquid crystal material and polymer decreases in polymerizing process, which causes phase separation of liquid crystal within polymer phase, and thereby to produce capsule-type particles with thermotropic liquid crystal surrounded by polymer. The obtained microcapsules (capsule-type particles) can show behavior of liquid crystal as it is within polymer phase.
In addition, the present thermotropic liquid crystal polymer microcapsules can be applied as a stabilizing media for active ingredients by loading the active ingredients within the liquid crystal phase. In this case, by adding copolymer having crosslinkable functional group in suspension polymerization step, the polymer surrounding liquid crystal can be crosslinked, and the result, active ingredients within the liquid crystal can be completely protected from external irritation.